Inductors are placed in circuits with one or more semiconductor devices, for performing actions such as filtering and RF matching. An inductor usually contains one or more turns of a conductor, around an air core or magnetic core, and the value of the inductance is directly proportional to the amount of the magnetic field coupled to the turns of the conductor due to an alternating current flowing through that conductor. Small value inductors, which do not require a large area, can be realized on-die a silicon chip, to reduce the BOM and to save on the real-estate on printed circuit boards (PCBs). Such inductors can also be patterned on the metal layers of an IC packaging substrate and connected to the circuitry on-die with a path with low electrical parasitics. However, when the value of the inductance needed is large (e.g., in a bulk inductor at the output of a voltage regulator), such on-die or on-substrate metal patterns with a non-magnetic medium surrounding them, could be cost prohibitive or practically impossible within the die structure.
Magnetic core material is used in surface mount discrete inductors, over which wires are wound, for realizing high value inductors for applications such as power supply filtering. Such magnetic core inductors are often placed on a PCB, side-by-side with the semiconductor device, due to their large footprint and thickness. Low profile magnetic core inductors are gradually becoming available for surface mounting on the top layer of the IC packaging substrate, side-by-side with the silicon die. However, their footprint may still cause the IC packaging substrate size to grow.
Radio frequency (RF) circuits including RF transceivers may utilize high quality passive devices such as inductors. For example, integrated passive devices (IPDs) can be used as surface mount integrated circuits. Using inductors as surface mount devices, however, may necessitate additional surface mount technology (SMT) process steps, and may lead to a larger sized interposer, resulting in an increased cost. For example, additional surface area on a touch-sensitive interface (TSI) surface for surface mounting passive components, and/or the use of special soldering process for mounting small (e.g., <0.4×0.4×0.4 mm) passive components may be unavoidable.
Air core inductors on TSI redistribution layer (RDL) metals may have a low Q-factor (e.g., ˜10-25 for inductance range ˜1-10 nH at 2 GHz) and a high cost due to deep via etch and fill on silicon wafer, and, planar spiral inductors may be costly due to the high cost of RDL metal layer. High current inductors may typically be in the form of bulky discrete components and located on PCB or package substrate. However, the large current needed to feed the PCB or substrate traces connected to the chip power supplier pins may cause issues with power loss and power supply integrity.